Telephone or like system



April23, 1946. c. GILLINGS ETAL TELEPHONE EOR LIKE SYSTEM 6 Shets-Sheet2 W ED s LAWRENCE JOHN MURRAY BY a g ATTOR NEY April 23, 1946 c.GILLINGS ETAL 2,398,826

TELEPHONE OR LIKE SYSTEM Filed Feb. 5, 1944 6 Sheets-Shet 5 FSM , spasPsu S/A' 1pa3 1pm a2 d2 013 1pa4 1pd4 d 1 Hm 2o d4 INVENTORS CHARLESGILLINGS LAWRENCE JOHN MURRAY ATTORNEY April 23, 1946.

C. GILLINGS ETAL TELEPHONE 0R LIKE SYSTEM Filed Feb/s, 1944 y eSheets-Sheet 4 HWP NVENTORS CHARLES, GILLINGS LAWRENCE JOHN MURRAY ATTORNEY April 23, 1946; c. GILLI NGS ETAL 2,398,826

' TELEPHONE OR LI E SYSTEM Filed Feb. 3, 1944 6 Sheets-Sheeti 6pp3 GPPZL\1PP2 n INVENTORS 6 CHARLES GILUNGS V LAURENCE JOHN MURRAY v ATTORNEYPatented Apr. 23, 1946 2,398,826 TELEPHONE R LIKE SYSTEM CharlesGillings and Lawrence John Murray, Liverpool, England, assignors toAutomatic 12,398,826. FlCE Electric Laboratories, Inc., Chicago, 111., acorporation of Delaware Application February 3, 1944, Serial No. 520,910In Great Britain March 8, 1943 10 Claims.

The present invention concerns improvements in or relating to telephoneor like systems and is more particularly concerned with crossbarswitches as described for instance in our applicasecondary preselectionstage of a four-digit automatic telephone system of the above-mentionedtype, the stage concerned being assumed to serve the sixteen hundredsubscribers numbered 3111-4600.

Fig. 2 shows two out of the possible four columns of primary crossbarswitching units which together form the primary part of the primary/secondary preselection stage of Figwhile it also indicates the relays ofthe associated control equipment which are representative of thecolumns, of the sub-columns and of the primary switching units. Thesecontrol equipment relays are arranged in a number of chain circuits, se-

lected ones of which are included in the circuits of theprimary/secondary preselection stage shown-in Figs. 3-6 when arranged inthe manner indicated in Fig. 5a.

1 Referring now to the trunking diagram, the

45 her of lines in 50 involved are assumedto range from 3111-4600 m i nary preselection stage; which c 60 prises a number of relativelysmallcapacity primary and secondary crossbar switching units suchasPSUl/A and SSUI, enables a subscriber, on removal of his receiver, tobe automatically cont on Se al O. filed Dec. 8, 1943. 5 nected to afirst numerical group selectmg-cross- In the prior specification controlequipments bar switching unit. As W111 be appreciated later, areprovided involving relays and simple unia preselection stage may servebetween two hundirectional switch mechanisms or uniselectors in dred andsixteen hundred subscribers lines acassociation with each of the variousswitching cording to the traflic involved. and it connects stages. witha group of six i'lrst numerical group select- It is an object of thepresent invention to prog units, each of WhlCh 1s capable'of har g pvide arrangements for selecting an idle line in t; ter; connections andso has ten links incoming the rou ,for instance, preselectingarrangements t ere o.- whiih eilploy control equipment including onlyEach o e prlmary me umts s a relays but it must be understood that theinvenily anged to accommodate twen y subscrlbeljs tion is notparticularly limited to arrangements and to have access to slx outlets,each of WhlCh is d sclosed in the above system. lmked with a secondaryswitching unit. Up to According to the invention, in a telephone 5375-twen y prim ry units may be arranged in a coltem employing crossbar typeswitches, the conumn and from one to four columns, according to nectionof any one of a nu b of lines t an the trafiic density involved has orhave access to idle line of a second group of lines is effected by agroup of SIX secon ry un s S e h exciting a plurality of relay chains,the relays of 1 termmates twenty s from the p one of which chainscorrespond t th individual mary units and has access to ten linkstoiirst lines, and the relays of another of which chains oup selectlngse st a d nti th correspond to the individual groups of lines into pyunits ITSUI/A and PSU20/A of the first which the said first lines aredivided, which relay Column d .u s SUI/ and PSU2 0/D of the chains causecrossbar switching mechanism, for fourth Column are shown in the drawmsinstance primary and secondary crossbar select- A group of s xfirstgroup selecting units thus ing units, to be operated substantiallyinstanves up to four columns of primary units. If taneously to connect aline of said first group to the tmflic ty 18 ht, t en the maximum of anidle line f said seco d grgup The invention four columns will beprovided and twenty subis particularly applicable for the connection ofscr1bers will be accommodated per primary unit subscribers lines to anidle line leading to the so that unde? these the X firstiselect first nm rical switching stage. ing units will be. serving sixteen hundred sub-The invention will be better understood from sfinbers 111161? Undel: Yheavy o ndithe following description of one method of carryeach p imaryunit might be adapted only to ing it into effect, reference being had tothe acaccommodate ten stlbscn'bers" and one companying drawingscomprising Figs, 1 t umn might be provided so that the six selecting Ofthese figures Fig, 1 h w t essential units would now be serving twohundred subtrunking arrangements of an all-relay primary/ Sen-hers onlyyaltering the number of columns,

the number of primary switching units in a columnand the number ofsubscribers lines per primary switching unit, the Dreselection stage maybe adapted to accommodate a suitable numaccordance with the trafilcinvolved.

Inthe drawings where the maximum of sixteen hundred subscribers isassumed'tobe served by the preselection stage, the subscribers numbersinclusive.

As regards the construction of the crossbar primary units, these eachcomprise three two-way horizontal selecting or prepare bars togetherwith three pairs of associated bar controlling relays lPP, ZPP, GPP,which connect with the six outlets concerned. In addition there aretwenty vertical holding bars and associated controlling relays lPH-20PHwhich connect with the twenty subscribers lines concerned, and by meansof .,...1W. l b-c-Q u n r ams 9P ence'uponpolumn relayf'A'and withprimary unita 'relay IPA operated, then primary unit PSUl/A which atdariedu'd can be completed between a calling line and any one of thesix outlets available to a primary unit. Similar remarks apply asregards the secondary units with the exspectively, the four sub-columnsof column 2 employing the relays BABD (not shown) and so on. For eachprimary unit there is provided a control relay; fo the first column,relay 'IPA serves unit PSUl/A,

relay ZPA serves unit PSUZ/A and so on upto'relay ,ZBPA. In the fourthcolumn the, relays will be designated [PD to; ,.2 PD for the primaryunits PSUl/D- PSIJZU/D. The primaryunit. relays of each sub-column, thesub-column relays of each column, and the column relays arearrangedin anumber of chain ci,rcuits,,,the general operation .c-twhich is asfollows, when 70118101, more subscribers in the primary/secondarypreselection stage originates a c a1l.

, If a call is originated'om-jsay. unitPSUl/A, the

. chain circuit. involvin'gthe five relays IPA5PA in thesub-columnconcerned comes into operationand relay IPA associated with unit PSUl/Aoperates toipick out the .callingunit PSUl/A.

; .nsimilar operations can betaking place simultaneously for each. ofthe sixteen sub-columns ,in the primary/secondary group if calls arebeing originatedin. these sub-columns.

The chaincircuit involving the column relays i A-.D now comes intooperation to pick thecallingcolumn out .ofthegroup'of four such columns..Where more than onecolumn is calling, then onecolumn onlyj'willbepicked out.

jIfhe, chain circuit involving the sub-column .relay's of, the selectedcolumn now comes into ,operati on to determine, the. calling sub-column.

It more than .o'nelsub-column is calling then oneonly of thesub-nolumnswill b picked out. It may be; mentioned that the reason why a particularcalling-primary unit isnot picked out by connecting all the relevant PArelays in a chain circuit or why a particular one out of the sixteenpossible calling subecolumhsisnotpicked out by connecting the sixteenrelevant relaysAA-DD .in a single chain circuit,;is that it is desirablenot to have 1300f manyv relays in a single simultaneous outlet testingchain circuit of the'type to beemployed since thefirst one of a chainin' operatingmay have to break operating circuits for all;- theGthBIfIElaYSOflhB Chain. With too. many relays in the chain arcing willoccur at the relay contacts with serious results.

" :.,The. three above stages of chain selection are,effectedfalmostinstantaneously and as a result there willbe operatedone column relay, one of the sub-columnrelays in that column and one ofthe primary unit relays in'that sub-column; in ddition there, may. be aprimary unit relay operatedin other subcolumns.

eratedin dep endrelays. l proper whi ch are closed at the intersectionof anygiven pair of vertical and horizontal bars,

will be pickedfout as the unit which is to be connected through to asecondary unit.

If calls have also been originated on other primary units, then in caseswhere these units are in sub-columns other than the sub-column selected,the operation of one of the set of relevant primary unit relays will bewithout avail, while in the case Where these units are in the sub-columnselected the relevant primary unit relays will not be allowed to operatein view of the operation of relay IPA which in so doing disconnectstheir operating circuits.

When primary unit PSUl/A is picked out in the above described manner,then the six prepare relays |PP6PP on this unit which are also connectedup in a chain circuit are caused to test for an idle one of the siXavailable outlets to a secondary unit. When a secondary unit is takeninto use its ten prepare magnets lSP-lU-SP which are connected in achain circuit are caused to test for an idle one of the ten possibleoutlets to first numerical selectors, and when a free outlet is foundthe calling party is switched through to the selector. At the same time,the control equipment is released, whereupon, if a further call iswaiting to be put through, the cycle of operations is repeated.

Theoperation of the various chain circuits will be appreciated from theensuing circuit description of a call originated by a subscriber No.3111 on primary unit PSUl/A, the line circuit concerned being shown inFigure 3. For convenience it will be assumed that when this subscriberremoves his receiver he will be automatically connected through to thefirst of the sixty available selectors over the first vertical internallink of primary unit PSUl/A over the first of the six available externallinks to'secondary units and then via the first vertical internal linkof secondary unitSSUl In the circuits the number of contact unitscarried by eachrelay is shown beneath its designation, as for instance(Fig. 3) for relay A, the contact units being designated individuallyinsrnall letters which in this instance will be ctl a2, a3 and a4.

As regards the crossbar vertical and horizontal relays, these areindicated by a hatched'rectangle, the contact units individual theretobeing indicated in the same manner as for ordinary The set of crossbarswitch contacts say'thecontacts controlled by magnets [PH and lPP onprimar'y switching unit PSUI /A, are designated FP 1 according to theset. of c'ontacts'involved.

. ,When subscriber No. 3111 'on'primary unit PSUl/A originates a call,the loop placed by his I telephone across the left-handset of negativeand positive conductors (Fig. 3 operatesline relay IR which in so doingat contacts lrl disconnects the standing idle marking battery viaresistance YA and extends a guard earth on to the incom ing test'lead Tfrom'the final "'sele'ctormultiple FSM or its equivalent. At contacts'lfZ it'starts up the so-called fprimar'y control chain circuitinvolving relays IPA5PA, associated respectively with the sub-column ofprimary units PSU I /A-PSUI /D, so as to determine whether the primaryunit PSUI/A concerned or whether another calling primary unit in thesame sub-column shall be picked out as the one through which a call isto be extended to aselector at this time, it being appreciated that onlyone call can be dealt with at a time by the control equipment. Inaddition to this chain circuit there are fifteen similar circuits forthe fifteen other sub-columns in the four columns of primary units andin-each of these one of the primary unit relays may be operated if callsare originated at this time.

It should be explained that corresponding contacts Ir2 2ilr2 of therelays IR2IJR allocated to primary units PSUI /A-PSU5/A are given thesame references in Fig. 3 for the purpose of convenience. It willreadily be seen from their location in the chain circuit to which relaysthey belong. I

Referring again to the primary control chain involving relays IPA-EPA,and assuming that none of the units PSU2/A--PSU5 are originating a callat this time, then relay IPA will operate over the following circuit:earth, chain connected contacts Ina35pa3, contacts IIpaZ, ITZ and Ipgbl, winding of relay IPA to battery. In connection with the contactsIr2 it will be understood that in parallel with these contacts are thecontacts 212-4012 of the nineteen other line relays 2R-2HR of thenineteen other subscribers on unit PSUI/A. Relay IPA in operating locksover its make-first light contacts IpaI, at contacts IpaZ opens itsinitial operating circuit and at contacts Ipa3 opens the operating pathfor any of the other relays ZPA-EPA. Had another PA relay, say relay ZPAof unit PSUZ/A, attempted to switch at the same time as relay IPA, itwill be seen that the latter in operating would have disconnected relay2PA since the operating circuit for this other relay is completed overcontacts Ipa3. Unit PSUZ/A would then have had to wait until the call onunit PSUI/A had been put through. Relay IPA thus has precedence overrelay 2PA; relay 2PA over relay SPA and so on.

Returning now to the operation of relay IPA, this relay in operating atits contacts IpaA (Fig. 3) starts up thecolumn chain circuit involvingrelays A--D and it will .be noted that the contacts Ipa420pa4 of therelays IPA-2IlPA are associated with the column I relay A. If at thistime relay IPA is the only one calling, then relay "A will operate andwill lock over its contacts aI, disconnect its operating circuit atcontacts a2 and at contacts a3 will prevent any of the other relays BDfrom coming in. In the event of there being simultaneous calls from twoor more columns, it will be seen that relay A will have preference overrelay B, relay B over relay C, and so on.

With relay A operated it is nOW possible due to the closure of contact al to determine which of the four sub-columns in column I shall be putthrough and this is effected by the sub-column discriminating chainshown in Fig. 5 and involving relays AA-AD. Associated with sub-columnrelay AA are the contacts Ipa5-5pa5 of the relays IPA-EPA and assumingthat a call has originated only from thefirst sub-column, relay AA willoperate and at its contacts aal will lock and at its contacts aa2 and M3will open its own operating circuit and will prevent any of the otherrelays AB-AD from coming in. V

With relays AA and IPA operatedlthe calling primary switching unitPSUI/A is now caused to test over-the six available outgoinglinks'tothecults of the five primary units PSUI /A-PSU/A,

andth'en via contacts I p116 to start up the chain circuit of unitPSUI/A. The test lead for the first of the. six available outlets fromthis unit is designated II, and if this is free, battery via resistanceYB (Fig. 6) will be encountered thereon and relay. IPP will operate.This relay in operatinglocks at its contacts I ml, and at its contactsIpIpZ and Ipp3 opens its own energizing circuit and also any operatingcircuit for any of the other five relays 2PP-BPP. Relay IPP in operating also actuates its horizontal bar. If two or more outlets are free,say the first and second, relay IPP will have preference over relay 21Fand so. on.

a From Fig. 1 it will be seen that the first outgoing link from unitPSUI/A gives access to secondary unit SSUI and hence relay IPP inoperating, at its contacts Ipp4 (Fig. 5) will extend earth overcommon'lead I3 to energise the start relay SS of secondary unit SSUI Asexplained in connection with Fig. 1, unit SSUI serves twenty incominglinks fromthe primary units, and each link may be shared by up to fourprimary units so that the common start lead I3 will therefore be-commonto the contacts Ippll of the relays IPP on all the primary switchingunits up to eighty) in the primary/secondary group. As regards test leadII, this will be common to the relays IPP in the four primary unitssharing access to the first vertical internal link on secondary unitSSUI, while as regards lead I2, this is common to the contactsIshZ-ZflshZ of the Vertical holding relays ISH-2IISH on unit SSUI,common leads equivalent to II terminating. on the other side of each ofthe contacts 2sh220sh2 in the same manner as for contacts IshZ. The linkbusying function of the contacts Ish2--2 0sh2 will be dealt with later.

Returning now to the operation of the start relay SS for secondary unitSSUI, in order to gain access to a free first numerical selecting unitit is now only necessary to pick out one of the ten outgoing leads fromunit SSUI. Relay SS in operating, at its contacts SSI-SSIO (Figs. 6 and4) closes chain circuits for. the ten relays ISP-IBSP on unit SSUI, andthese relays each test for a free outlet. To avoid having all the ten SPrelays in one chain they are divided up into two interlinked chaincircuits, the arrangements of each chain circuit being the same as thosealready described in that the first relay of the chain gets preferenceover the second, the second over the third, and so on. The interlinkingarrangements between the two chain circuits are such that if any of therelays in the chain involving relays ISP5SP- operate, then the secondchain circuit willbe disconnected at one or other of the contacts Ispl-Espfl and vice versa; Considering the operation of the first chain, onoperation of relay SS, earth is connected up over the chain-connectedcontacts 6sp4-I0sp4 and Isp3-5sp3, contacts IspZ, relay ISP, contactsssl and lead I4 which connects up with the test lead T of the first ofthe ten links extendingrrom the unit SSU I. The other" relays2SP-5SP"are connected up to'si milar test leads of other links, ldesignating the test leadfor the fifth available link, while in Fig. 4leadslB and I1 respectively designate the sixth and tenth available testleads.

If the first of the available ten links is free, then relay ISP willoperate in series with theidle marking resistance battery Which will benormally connected at the terminating" group selecting unit to lead T,and at contacts l-spl; will look, while at its contacts I sp2-lsp4 itwill open any operating circuitfor all other relays both in its ownchain circuit and in the other'chain'circ'uit of Fi in operating it alsoactuates'itshorizontal bar. At contacts lsp5 (Fig. 4) an earth isextended on to lead [8 which is common to the ,contacts lsp5-lllsp5 ofall ten SP relays on'the unit SSUI, and relay SZ operates.

Relay SZ in operating at contacts szl (Fig. 4) extends earth on tocommon lead Z2 which is equivalent tothe start lead l3 (Fig- 6) inthat'it V is common to the contacts re s of the relays IPP on all(eighty) of the primary units in the primary/secondary group, thecontacts lpp5on primary units PSUI /A- PSU| /D connecting on their otherside with relay ISH, the corresponding contacts onunitsPSUZ/A-PSUZ/Dconnecting with relay 28H and so on up-to contactslppionunits PSU20/A-PSU2fl/D which connect with relay 20SH. Only one PPrelay'can be operated, however, at this time, inthis instance relayI'PP'on primary unit PSUl/A, and hence only the first vertical holdrelay l SH on unit SSUl will be operated. Relay lSH in operating, at itscontacts sh-I prepares a locking circuit on to the hold lead H andactuates its associated first vertical bar on unit SSUI, so that the setof contacts at the intersection of the vertical and horizontal bars inquestion will be operated; these are shown as ISH 1SP' in Fig. 4. RelaySZ in operating also atcontacts s22 (Fig. 4) extends earth via the lowresistance lower winding of relay'Z on to lead !-9 which is commonto-the contacts aa5dd5 of the sixteen subcolumn relays AA -DD. In thisinstance relay AA is operated so that the circuit will be extendedthrough to common lead 20 which. is common to the contacts lpa'l-Epdl ofthe five relays iPA- --5PA of the primary units in the sub-colu'm'nserved'by relay AA. In this instance relay= IPA is operated so that thecircuit is'ext'ended through to common lead 21 which is common to thecontacts lr3--2llr3 of the line relays l'R-ZOR of the twentysubscribers'numbered 3i H-SIZD: served by primary llIlit'PSUfl/A. Inthis instance contacts H3 are operatedysignifying a call 'fromsubscriber No. 3111.,"S0l that the circuit is extended through tothevertical: hold relay IPH associated with this subscriber. If relay23R had been operated instead'of relay IR signifying a call fromsubscriber No. 3120, then the circuit would have been established torelay ZQPH. In case. two or more line relays are operated, line relaylRJWill receive preference over line relay 2R, relay 2R over relay SRand so on up to 20R. 7

In the present instance relay [PH in operating actuates its associatedvertical bar, whereupon since relay IPP has already operated,thecrossbar contacts IPH lPP

are closed and extend the calling subscribers loo-pthrough to the firstof the six selecting units available-from unit SSUI. Relay [PH inoperating, at its contacts Iphl completes a temporary lockin'gcircuitfor itself over contacts 1PH lPP 'at contacts 22 (Fig. 3) the columnchaincircuit involving relay A-D is opened to release the previouslyoperated relay A and at the same time to prevent the chain circuit againcoming into operation or being maintained in operation in response toother calls originated at this time. Relay A in releasing releases theoperated subcol'umn discriminating chain for column I, involving relaysAA- AD, and relay AA in releasing, at-contacts call (Fig. 5) releasesthe secondary unit' test chain involving the relays |PP6PP of primaryunit PSUl/A. Relay IPP in releasing, at contacts mp4 (Fig. 5) opens thestart circult to relay SS of unit SSUI and also at contacts lpp5 Fig. 4)opens the local holding circuits for relays I SH, lPl-I and l K. By thistime, however, a guarding and holding earth will have been returned overthe H lead from the selecting-unit taken'into use so that these relayswill remain held throughout the connection. Relay SS in releasing'opensthe secondary unit outlet test chains involving relays lSP-ESP and 6SP IUSP, whereupon the previously operated relay 1 SP releases and in sodoing at contacts 'lspS (Fig.4) releases relay SZ. Relay SZ inreleasing, at contacts s23 (Fig. 4) releases relay Z, whereupon theearth. feed to the column chain (Fig. 3) is restored at contacts .922,and the equipment is now readyto handle the connection 'ofanothercalling party to a free one of the sixty selectors available to theprimary/secondary stage.

On release of the prepare relays IPP and l SP, the-associated horizontalbars which were operated will have released, but the pins or theirequivalents which were engaged by the actuated vertical-bars remain heldwithout appreciably restraining the restoration of the horizontal bars.

Relay I SH in remaining operated, at its contacts Ish2 (Fig. 6) marksthe first vertical internal link on unit SSUI as busy so that subsequentcalls through this unit must be routed through one or other of the links2-20 via their corresponding vertical hold relays 2SH-2ilSH.

'At the same contacts unit SSUI is busied as far as a subsequent callfrom any of the units PSUl/APSUl'/D are concerned, since these unitshave accessfonly to the first vertical link on unit SSUI via'thejfirstof the siX available linksto secondary units.

From thef'oregoing description it will be seen that of the up to sixteenhundred subscribers accommodated in the primary/secondary stage onlyone, call at a time can be handled by the all-relay chainswitching'control equipment, other'calls originatedat this time havingto wait. till they ca be picked out one by one'by the control equipment.The connecting process for each call is, however, almost instantaneousso that the waiting time for any calling subscriber before a diallingtone is received from a first numerical selector or its equivalent willnever become excessive.

Referring again to the trunking diagram of Fig. 1, and again consideringa call originated by subscriber No. 3111 on unit PSUl/A, connection witha group selecting unit cannot be effected, firstly if all the sixavailable links to secondary units are directly busied due to theoperation of the relays ISH in each of the six secondary unitsSSUl-SSUB, while furthermore, any one of the links can be indirectlybusied owing to the fact that on the associated secondary unit all tenoutlets therefrom to first numerical selecting units are already in use.

In the first instance, with the relays ISH in all the units SSUI-SSU6 inan operated condition, the series-connected contactslsh3 (Fig. 6) oneach of these relays will bring up the busy relay IPGB associated withthe six links available to switches, each of said relay chainscontaining a plurality of relays corresponding respectively to thedifferent crossbar switches in the associated group of switches, afurther relay chain containof said crossbar switches to connect thecalling subscribers line to one of the trunks terminating in thatswitch.

2. In a switching system, a plurality of groups of crossbar switches,each of said switches having a plurality of incoming lines and aplurality of outgoing lines, a relay chain for each group of switches,each of said relay chains containing the four units P-SUI /A-PSU| /D.Relay IPGB in I operating, at its contacts I pgbl (Fig. 3) disconnectsany circuit to relay IPA thus preventing further calls from subscribers3| l l--3l20 on primary unit PSUl/A from being dealt with, while inaddition other contacts lpgb2-lpgb4 (not shown) will disconnect relaysIPB-lPD from their relevant primary control chain circuits so as toprevent the subscribers on the units PSUl/BPSUl/D from setting upconnections.

Any one of these eighty subscribers must therefore wait until one of thesix links, available in common to their primary units, becomes free.

Similar remarks apply to the sets of six links available to otherprimary units, relay ZOPGB (Fig. 6) serving the units PSU20/APSU2ll/D.

In the second instance, if all ten outlets from secondary unit SSUI areengaged, all links thereto from the primary switching units are busiedin the following manner. For each secondary switching unit a group busyrelay is provided, re-

tioned here that rectifiers such as MBA and MR3 are provided to preventmutual interference between the outgoing test leads to which relay IGBis connected.

Relay IGB in releasing at its contacts lgbl brings up relay ISGB whichis individual to the unit SSUI and this relay in operating, at itscontacts I sgbzl disconnects the idle marking resistance battery fromcommon lead l2 so as to mark all twenty of the incoming link test leadsas busy. At contacts lsgbl-lsgb20 it simulates the operation of all therelays ISH-ZOSH on unit SSUI to prepare for the operation of one orother of the busy relays IPGB to ZBPGB when the requisite conditionsobtain.

What we claim as new and desire to secure by Letters Patent is:

1. In a telephone system, a plurality of groups of crossbar switcheseach having a plurality of subscribers lines and a plurality of trunksterminating therein, a relay chain for each group of a plurality ofrelays corresponding respectively to the different switchesin theassociated group of switches, a'further relay chain containing aplurality of relays corresponding respectively to the different groupsof said switches, means controlled over any one of said incoming linesto operate a relay in said last chain and a relay in one of said otherchains, and means controlled conjointly by said two operated relays tooperate a particular one of said crossbarswitches to connect said oneincoming line to an idle one of the lines outgoing from that switch.

3. In a system as claimed in claim 1, means in each relay chainpreventing the concurrent operation of any two relays in that chain,thereby to prevent connections from being completed simul taneously byany two of said cross-bar switches.

4. In a switching system, a plurality of crossbar switches arbitrarilydivided into groups and subgroups, each of said switches having aplurality of. incoming lines and a plurality of outgoing lines; asubgroup relay chainfor each subgroup of switches, each of said subgroupchains containing a plurality of relays corresponding respectively tothe different switches in the associated subgroup; a group relay chainfor each group of switches, each of said group chains containing aplurality of relays corresponding respectively to the differentsubgroups in the associated group; a system relay chain containing aplurality of relays corresponding respectively to the different groupsof switches; and means controlled over any one of said incoming linesfor operating a relay in said system relay chain,

a relay in one of said group relay chains and a relay in one of saidsubgroup relay chains, thereby to operate a particular one of saidcrossbar switches to connect said one incoming line to an idle one ofthe lines outgoing from that switch.

5. In a switching system, a plurality of groups of crossbar switches,each of said switches having a plurality of incoming lines and aplurality of outgoing lines, a plurality of primary relays correspondingrespectively to the different ones of said switches, a plurality ofsecondary relays corresponding respectively to the different ones ofsaid groups, means normally controlled by a calling condition on any oneof said incoming lines for operating the primary relay corresponding tothe particular crossbar switch in which that line appears and alsooperating the secondary relay corresponding to the group in which saidparticular switch appears, means controlled by said two operated relaysfor operating said particular crossbar switch to connect said callingline to one of the lines outgoing from said particular switch, andmeanspreventing the concurrent operation of primary relays which correspondto diiierent switches in the same group and preventing the concurrentoperation of difierent secondary relays.

6. In a switching system, a plurality of crossbar switches arbitrarilydivided into groups and subgroups, each of said switches having aplurality of incoming lines and a plurality of outgoing lines; aplurality of primary relays corresponding respectively to the differentones of said switches; a plurality of secondary relays correspondingrespectively to the difierent ones of .said subgroups; a plurality oftertiary relays corresponding respectively to the difierent ones of saidgroups; means normally controlled by a calling condition on any one ofsaid incoming lines for operating the primary relay, corresponding tothe particular crossbar switch in which that line appears, the secondaryrelay correspondingto the. particular subgroup in which said particularswitchappears, and the tertiary relay corresponding tov the group inwhich said particular subgroup appears; means including said threeoperated relays for operating said particular crossbar switch to connectsaid calling line to one of the lines outgoing from said particularswitch; means preventing the concurrent operation of any two primaryrelays which correspond to crossbar switches in the same subgroup; meanspreventing the concurrent operation of any two secondary relayscorresponding to subgroups in the same .group; and means preventing theconcurrent operation of any two of said tertiary relays.

7. In a switching system, a crossbar switch having a plurality ofincoming lines and a plurality of groups of outgoing lines, means foroperating said switch toconnec-t any one of. said incoming lines to anyone or said outgoing lines, said means including a plurality'of magnetscorresponding respectively to. said outgoing lines, a plurality of chaincircuits corresponding respectively to the different. ones. of saidgroups, each chain circuit including the magnets which correspond totheoutgoing lines of one group, means in each chain circuit preventingthe concurrent operation of any two of the magnets in that circuit, andmean-s interlinking, the difierent ones of said chain circuits topreventconcurrent operation of magnets in difierent chain circuits.

8-. Ina switching system, a plurality of primary crossbar switchesarbitrarily divided into groups, a plurality of individual relayscorresponding respectively to the diiierent ones? of said switches, aplurality of group relays corresponding respectively to the differentones of said groups, a plurality of secondary crossbar switches, aplurality of lines terminating in each of said primary and secondaryswitches, links extending from, each primary switch to every secondaryswitch, means controlled by a calling condition on any line terminatingin one of said primary switches for operating the individual relaycorresponding to the particular primary switch in: which the. callingline terminates and also operating the group relay. corresponding to thegroup inrwhich. that primary switch appears, means controlled by saidtwo operated relays, for selecting idlelink from said particular primaryswitchto any one of said secondary switches, and means-: for thereuponoperating said particular primary switch and said one secondary switchto complete a connection over said selected link from. said calling lineto one of said lines terminating in said one secondary switch.

9. In a switching system, a plurality of groups of primary crossbarswitches, a plurality of individual relays corresponding respectively tothe diiierent ones of said switches, a plurality of group relayscorresponding respectively to the difierent ones of said groups, aplurality of lines terminating in each of said switches, a plurality ofsecondary crossbar switches, links extending from each primary switch toevery secondary switch, means controlled by a calling condition on anyone of said lines for operating the individual relay corresponding tothe particular primary switch in which the calling line terminates andalso operating the group relay corresponding to the group in which thatprimary switch appears, means controlled by said two operated relays forselecting an idle link from said particular primary switch to any one ofsaid secondary switches, a plurality of lines outgoing from said onesecondary switch, means for operating said particular primary switchandsaid one secondary switch to complete a connection oversaid selectedlink from said calling line to one of. said outgoing lines, said lastmeans including a plurality of magnets corresponding respectively tosaid outgoing lines and a chain circuit for preventing the concurrentoperation of any two of said magnets.

10. In a switching system, a plurality of groups of primary crossbarswitches, a plurality of individual relays corresponding respectively tothe different ones of said switches, a plurality of group relayscorresponding respectively to the different ones of said groups, aplurality of lines terminating in each of saidswitches, a plurality of.secondary crossbar switches, links extending from each primary switch toevery secondary switch, means controlled by a. calling. condition on anyone of said lines for operating the individual relay corresponding tothe particular primary switch in which the calling line terminates andalso operating the group relay corresponding to the group in which thatprimary switch appears, means controlled. by said two operated relaysfor selecting an idle link from said particular primary switch to anyone of said secondary switches, a plurality of groups of lines outgoingfrom said one secondary switch, means for operating said particularprimary switch and said one secondary switch to complete a connectionover said selected link from said calling line to one of said outgoinglines, said last means including a plurality of magnets correspondingrespectively to said outgoing lines, a plurality of chain cir cuitscorresponding respectively to the different ones of said groups oflines, each chain circuit including the magnets which correspond to theoutgoing lines of one group, meansin each chain circuit for preventingthe concurrent operation of any two magnets in that circuit, and meansinterlinking thed'iif'erent ones of said chain circuits to preventconcurrent operation of magnets in different chain circuits.

CHARLES GILLINGS. LAWRENCE JOHN MURRAY.

